Williams wall heater produces black smoke

My girlfriend has a Williams Furnace Company wall heater and it produces black sooty exhaust that leaves black residue at the very top of the sheetmetal grate. The soot is not excessive but when it is left on the odor and smoke is enought to cause her concern.
We have tried to get the landlord to get it taken care of for the past three months and i am done waiting.

I spoke to a co-worker and he informed me that there is a metering screw which adjusts the mixture from lean to rich, he thinks it should be found at the base of the unit. If this is the case it seems to be too rich.

Im pretty good with figuring out how things work (and when i am in over my head) and plan on taking a look at it this evening. Before i do, can anyone offer any additional insight? Helpful tips and so forth?

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Usually this situation is caused by a vent that is not drafting or a burner that is misaligned and not burning clean (yellow flame). There is not a metering device on these heaters. Don't risk your girlfriend's safety. Get this repaired pronto -- this can be a serious situation.